Nowadays the consumable-electrode arc welding in shielding (oxidizing and inert) gases is the most widely used method of welding in the industry. In construction and on erection sites there is used unshielded consumable-electrode arc welding. Used as consumable electrodes are electrode wires of solid section and electrode wires having inner cavities filled with a powdered charge. A solid-section wire is essentially a homogeneous monolithic long metal rod. The electrode wire having inner cavities is a composite material comprising a thin-walled metal sheath of tubular or more complex section, and a charge. The charge enclosed in the inner cavity defined by the electrode wire sheath is a mechanical mixture of metal powders (iron powder, ferroalloys, alloying powders), slag-forming and stabilizing constituents. The ratio of cross-section area of the charge-filled cavity in the electrode wire having inner cavities to cross-section area of the whole wire usually equals from 0.5 to 0.8.
In welding with the use of solid-section wires both in shielding gases, especially oxidizing ones, and without additional shielding there occurs an increased spattering of electrode metal, as well as an unsatisfactory weld formation. To prevent formation of pores in the process of welding low-carbon and low-alloy steels, the electrode wires of solid section obligatorily comprise deoxidizers such as silicon, manganese, titanium, aluminium, having a closer affinity for oxygen than iron, as well as in some cases alloying constituents such as chromium, vanadium, molybdenum. The deoxidizers and alaloying elements present in the electrode wire worsen its ductility, make the process of manufacturing a small (0.6 to 1.6 mm) diameter wire needed for welding more complicated and expensive. It should be noted that the better quality of weld metal is required, the greater amount of alloying and deoxidizing elements will be contained in the wire and the lower will become its ductility (deformability). However, the presence of any of presently known combinations of alloying and deoxidizing elements in the composition of the solid-section wire fails to prevent spattering of electrode metal, as well as to substantially improve formation of a weld surface when welding in the shielding gases and to provide the required performance of the weld metal when using unshielded arc welding.
The electrode wires having inner cavities filled with the charge make it possible to obtain quality welds featuring high performance both in gas-shielded and unshielded arc welding. Ability of the electrode wire having inner cavities to deform in the process of cold working changes but slightly with a greater or smaller amount of alloying constituents present in the charge. However, in contrast to the solid-section wires the electrode wires having inner cavities are difficult-to-manufacture and need special feeding mechanisms having several pairs of feed rolls and applying inconsiderable unit pressure on the surface of wire made, as a rule, of cold-rolled low-carbon steel from 0.15 to 0.5 mm thick. Metal powder constituents in the composition of the charge of the electrode wire, mixed with slag-forming constituents are susceptible to corrosion, which limits the storage life of such wires; therefore the welding process with use of the electrode wire having inner cavities is insufficiently reliable for obtaining high-quality welds.
The charge of the electrode wire having inner cavities in spite of great amount of metal constituents (iron powder and ferroalloys) present therein does not conduct electric current and therefore, in the process of welding with use of such a wire, melting of its core considerably lags behind melting of its metal sheath. As a result of insufficient heating voluminous portions of the charge pass into a welding pool without melting-down, which decreases the effectiveness of a slag shield of droplets of molten metal in the process of their growth at the electrode end face and transfer into the welding pool, i.e. some part of the slag does not participate in protection of the molten metal from the atmospheric air. Thus the self-shielded electrode wires having inner cavities contain from 15 to 20 mass percent of shielding slag-forming materials in the charge which results in a lower welding efficiency thereof compared to solid-section wires.
Deformability in manufacture of the electrode wire having inner cavities is substantially lower than that of the solid-section wire as the thin-walled sheath whose strength is limited when being deformed should take a load produced by both the resistance to deformation of material of the sheath and resistance to deformation of the powdered change. Therefore, the process of manufacturing the electrode wires having inner cavities of small diameter is more complicated than the process of manufacturing the solid-section wires.
An increase in the melting efficiency of the electrode wire with maintaining good welding and fabrication characteristics of the electrode wire having inner cavities may be achieved in case of using a wire comprising a metal body incorporating alloying and deoxidizing constituents and a powdered charge located in longitudinal ducts of the metal body.
Most similar prior art disclosing a subject matter closely associated with the present invention is GB, A, No. 1,481,140 describing an electrode with comprising an alloyed metal body having at least one longitudinal cavity filled with a charge comprising at least one constituent selected from the group consisting of slag-forming and alloying constituents.
As distinct from the solid-section wire such a wire features a minimum spatter and quality weld formation. Moreover, this wire has a sufficient stiffness since it is manufactured not from a strip but from a shaped blank and does not require the use of special multiple-roll feed mechanisms. However, it is impossible to manufacture said wire with a diameter less than 1.6 mm because of a low ductility of the metal body. But is known that to obtain welds ensuring serviceability of structures made of steels comprising alloying constituents is possible only with use of the wire with a diameter of 1.6 mm and less for welding. The low ductility of the metal body depends on alloying constituents present therein. The greater the mass of the alloying constituents, the lower is ductility of the metal body. The requirements for a constant chemical composition throughout the metal body volume do not allow hot working and heat treatment to be performed after cold working of the metal body. The high temperature causes the chemical composition of near-the surface layers of the metal body to change due to interaction with the ambient atmosphere. In such a case the 1.6-mm diameter wire will have a metal body with chemical composition thereof upset in more than half of its volume, which will adversely affect the quality of the weld. Thus, the wire should be manufactured by cold working. However, it is impossible to obtain the wire of so intricate configuration of cross section without additional heat treatment due to the low ductility of the metal body. Moreover, even if the main part of the alloying constituents necessary for welding is introduced in the charge of the electrode wire their losses amount to from 20 to 90 percent depending on the welding conditions and affinity of the alloying constituent for oxygen. Therefore, introduction of alloying constituents in the composition of the wire metal body impairs its deformability, and the presence thereof in the charge composition brings about considerable burn-out losses during welding.